1. Technical Field
This invention relates to a method at a microwave oven for controlling a boiling procedure, said oven comprising an oven cavity, a microwave source, a supply system for supplying microwaves into the cavity, a control unit for controlling power level and supply time of the microwaves supplied to the cavity, and means connected to said control unit for setting or calculating a boiling time of a solid or liquid type of foodpiece. The invention is also directed to a microwave oven, a microwave heating device and the use thereof for automatically performing a boiling procedure.
2. Technical Background and Prior Art
Prior art is represented by U.S. Pat. No. 4,791,263, disclosing a method of the kind mentioned in the introduction, in which heating starts with 70% of maximum power and proceeds until a gas sensor senses 65% change of an initial value. Based on the time used for reaching this value a time for continued heating is calculated, said heating proceeding at about 50% of said maximum power. At the end of this calculated time it is assumed that boiling has been achieved, being thereafter continued during two optional, fixed times at a power level which is predetermined. Thereafter the method proceeds to a keep-warm state at a further lower, fixed power level. From this is clear that the power level during the actual boiling is controlled in a so called "open loop" by the use of fixed times and fixed power levels.
The disclosed method has the drawback that maximum power is not used when starting the procedure thereby increasing the consumption of time, said drawback being of the same kind as shown by a generally known method, which means setting a power level of 3/4 of maximum power for example and heating during a predetermined amount of time. A further disadvantage is that the actual boiling takes place at a predetermined, fixed power level without sensing the progress of the procedure. This means that the food piece may be directly influenced by the microwaves to an extent which is too high, giving a consequent risk of overboiling, which furthermore means unnecessary consumption of energy.